Cystic fibrosis (CF) is a hereditary condition that affects cAMP regulated chloride channels in epithelial tissues due to a defect in the cystic fibrosis transmembrane conductance regulatory (CFTR) gene. CF is the most common lethal hereditary condition in Caucasian populations. Recently, a transgenic CF mouse model was developed that has no normal CFTR expression. In addition to phenotypic features like those seen in humans with CF, the CF mouse has abnormal enamel. Preliminary studies show that 100% of CF mice have chalky white enamel while control mice have normal enamel. Initial histological and biochemical studies indicate that the CF mouse enamel defect results from abnormal ameloblast function prior to completion of the maturation stage of enamel development. The CF mouse enamel shows retention of amelogenin and crystallite defects similar to those seen in human enamel affected with amelogenesis imperfecta. it is unknown if CFTR is expressed in developing teeth. Therefore, the purpose of the proposed research is to determine if CFTR is expressed in developing murine teeth, to establish the temporal and spatial distribution of CFTR expression and to characterize the enamel histologically and biochemically ina the CF mouse model. Mice from an established CF mouse colony with a CFTR mutation consisting of an in frame stop codon in exon 10 will be genotyped and used for this study. Teeth from normal and CF mice will be analyzed for CFTR mRNA expression using PCR. Developing teeth from 7 to 9 day old mice will be surgically removed, the mRNA isolated and examined for CFTR expression. The RNA will be analyzed using RT-PCR and primers specific for exons 9 and 10 of the CFTR gene. CFTR expression will be further evaluated and localized in developing teeth using in-situ hybridization. Teeth from CF and normal mice will be evaluated using light microscopy, scanning and transmission electron microscopy. The mineral content of CF mouse and normal murine enamel will be evaluated at different stages of development. The mineral per volume will be determined using density gradient columns and measuring Ca by atomic absorption and P by a colorimetric assay. The enamel proteins will be analyzed using amino acid analysis, SDS-PAGE and Western blots. Multiple antibodies will be used (anti-amelogenin, anti- albumin, anti-tuftelin) to characterize the proteins. The immediate goal of this investigation is to establish the mechanism leading to abnormal enamel formation in the CF mouse. This study will provide detailed characterization of the enamel structure and composition so that its appropriateness as a model for hereditary enamel disorders in humans can be determined. Apparent similarities of CF mouse a potentially valuable model for studying genetically altered enamel development. The long term goal of this research is to understand the developmental mechanisms of genetically altered enamel so that appropriate diagnoses and optimal therapies can be developed.